Semi-submerged vessels have been proposed or constructed in various configurations, several examples being shown and described in U.S. Pat. No. 3,623,444. In most of these vessels there is considerable internal structure which limits the use of the available space. The submerged hulls, for example, are usually limited to use as fuel tanks or for controllable water ballast systems. The superstructure above water can be arranged in any suitable manner and is readily accessible, but access to the submerged hulls is through the supporting struts, which are restricted by structural requirements.
Use of the struts for storage and for easy access to the hulls would greatly increase the useful space in the vessel, and would also allow the effective center of mass to be lowered for improved stability.